The invention relates to a clutch assembly. More particularly, the invention relates to a clutch assembly having a multi-piece inner or outer clutch ring.
One-way or bi-directional roller type clutches typically include a cylindrical inner ring seated within a larger cylindrical outer ring. The outer peripheral surface of the inner ring commonly includes cam surfaces wherein a plurality of rollers is seated along the cam surfaces between the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring. These clutches may also include biasing springs for biasing the roller along the cam surfaces. When the clutch is unlocked, it allows rotation of the inner ring relative to the outer ring. Conversely, when the clutch is locked, it prevents rotation of the inner ring relative to the outer ring by the binding action of the rollers moved along the cam surfaces between the inner and outer rings.
When the clutch is locked by the rotation and torquing action of the inner ring with respect to the outer ring, the outward force of the rollers puts the outer ring into tension. The tensile hoop stress on the outer ring is at a maximum its inner peripheral surface and decreases towards the outer peripheral surface. The clutch torque limit is typically due to the limit of hertz stresses and hoop stress between the rings. Typically, the hertz stress is highest between the roller or spragues and the race or cam surfaces. This torque limit, or capacity, is a function of race diameter, roller diameter, roller length, number of rollers, material selection, heat treatment, and other factors. Further, the failure mode for excessive hoop stress is typically in the outer clutch ring where there is also tensile hoop stress. It is less common, but still possible, to have compression hoop stress failures in the inner clutch ring or shaft. The hoop strength of a clutch is also typically a function of inner and outer ring diameter, thickness, material selection, heat treatment, and other factors.
Prior art one way and bi-directional roller clutches, sprague clutches, strut clutches, and the like, are made of isotropic material and each of the inner and outer rings is made as a single part.
It is desirable to provide inner and outer clutch rings with higher hoop strengths, such that the clutch capacity will be less limited by the hoop strength of the rings.
According to one aspect of the invention, a clutch assembly includes an outer ring having an inner peripheral surface. An inner ring is seated within the outer ring and has an outer peripheral surface. A plurality of rollers is seated between the inner and outer peripheral surfaces for selectively binding the inner and outer rings and preventing relative movement between the inner and outer rings. At least one of the inner and outer rings includes an inner sleeve mechanically coupled to an outer jacket with an interference fit such that the inner sleeve is in compression and the outer jacket is in tension, whereby the tensile hoop stress is reduced between the inner and outer rings upon the binding of the rollers between the inner and outer peripheral surfaces.